The invention relates to piston-type injection pumps adapted to supply fuel to nozzle-type injectors in diesel engines, and more particularly to injection pumps of this general type which have facilities for providing pressure relief in the discharge conduit between the pump and the injector after the piston pump has completed its pressure stroke.
In certain known types of injector pumps of this general design, the pressure regulating facilities are in the form of discharge valves that ideally assure that sufficient pressure is maintained in the discharge conduit immediately after conclusion of the pressure stroke to prevent an undesired influx of gases from the engine combustion chamber to the fuel supply reservoir of the pump. Unfortunately, existing types of such discharge valves are bulky, complicated and generally unreliable.
As an alternative to such discharge valves, certain injection pump designs employ pressure-regulation facilities in the form of systems of throttling channels, usually in the fuel by-pass path of the pump. Such channels serve to increase backpressure in the discharge line. These arrangements have the disadvantage of being not only complex but also of yielding a rapid change of pressure with even small changes in the depth of the throttling channels. Additionally, when such expedients are used, it is observed that upon failure of the injector nozzle and/or shutdown of the injector, such throttling channels permit an undesired flow of combustion gases or residual pressurized air in the nozzle toward the fuel supply reservoir in the pump.